Unraveling sorption of lead in aqueous solutions by chemically modified biochar derived from coconut fiber: A microscopic and spectroscopic investigation

In this study, we examined the efficacy of nine different types of coconut-fiber derived biochars (CFBs), prepared at different temperatures and chemically modified with ammonia, hydrogen peroxide and nitric acid, to remove lead. (Pb2+) from aqueous solutions. Langmuir-q(m) values of the biochars pyrolyzed at 300 degrees C and modified with ammonia and nitric acid increased from 49.5 to 105.5 and 85.2 mg g(-1), respectively, compared to control (unmodified), whereas hydrogen peroxide treatment had no effect. The maximum amount of Pb adsorbed on biochars was in the order of CFB-700 > MCFB-300-NH3. H2O > CFB-500 > MCFB-300-HNO3 > CFB-300. X-ray absorption fine structure (XAFS) spectroscopy results revealed that Pb-montmorillonite, Pb(C2H3O2)(2), PbSO4, Pb-Al2O3 and Pb-3(PO4)(2) were the five most important Pb species observed in Pb-loaded biochars, and as such, favoring Pb immobilization in aqueous solutions. Overall, the sorption capacity of CFBs pyrolyzed at 300 degrees C substantially increased for Pb2+ with ammonia and nitric acid modification. However, these chemical modifications did not improve the sorption of Pb on CFBs pyrolyzed at temperatures >= 500 degrees C, thereby highlighting a temperature dependent response of chemically modified biochars to Pb sorption in this study. (C) 2016 Elsevier B.V. All rights reserved.